This invention relates generally to fasteners, and more particularly concerns improvements in rivet-type fasteners having certain unusual advantages in construction, mode of installation and operation.
Experience with conventional rivet retention of aircraft skins to fuselage structures has indicated several disadvantages and problems, particularly where fully tapered rivet heads are employed to seat in tapered counterbores or countersinks. Due to requirements, especially in aircraft assembly, that the head not protrude from the work surface at the completion of riveting; it has been the practice to drill deep countersinks ensuring full reception of the head in the countersink; however, this frequently results in damage to the work or skin surrounding the countersink, caused by impact of the tool that strikes the rivet head during rivet upset formation. Also, deep countersinks reduce the shear bearing area of the skin. In an effort to alleviate this problem, rivet heads have been formed to incorporate rearwardly facing central domes, an example being that in U.S. Pat. No. 3,927,458. However, the flattening of such domes or crowns during riveting can result in the formation of unwanted clearances between the rivet heads and work countersinks, as for example can occur due to creation of unwanted metal spring-back conditions.
Further, fluids can and do enter the gap or clearance to cause corrosion of the connection over a period of time, creating a dangerous weakening of the connection. In addition, it is difficult to paint over the gap or clearance without resulting in paint cracking. Finally, it is found in practice that it is very difficult to make the peripheries of such rivets exactly round, which aggravates the above problems.
The rivet in U.S. Pat. No. 2,237,338 to Dale is thickened at the extreme outer edge of the head; however, seating and separation problems are encountered, as described in that patent.
U.S. Pat. No. 4,086,839 to applicant herein constitutes a substantial improvement in rivet construction over the prior art in existence at the time of the invention thereof. There is need for further improvements in such rivets, and as to their construction and use, enhancing reliability and ease of installation.